During the manufacture of devices, such as optical modules for array cameras, manufacturing irregularities or manufacturing deviations may occur, for example, because of more or less unavoidable variations or inaccuracies in one or more of the process steps. For example, when the optical devices include one or more passive optical elements such as lenses, the devices may have focal lengths that slightly vary one from the other despite having the same nominal focal length. In some cases, the focal length may correspond to the flange focal length (FFL), or more generally, the focal length may refer to any focal length parameter (e.g., the effective focal length (EFL)). In any event, variations in the focal lengths can result in the focal plane of the lens system lying off the image sensor plane, which can lead to inferior image quality.
Another problem that can arise, for example, in array cameras is shifting of the optical axes of the various optical channels as a result of thermal expansion of the lens stacks. In some cases, thermal expansion can cause the various optical channels to shift laterally with respect to the image sensor plane. Thermal expansion also may cause the optical channels to become tilted with respect to the desired optical axis. Thus, thermal expansion also can lead to inferior image quality.
Additional problems that can arise relate to the use of adhesive in the optical assembly and/or tilt of the barrel lens or optical assembly. For example, a lens barrel or optical stack may be attached to a transparent wafer with adhesive, or an optical assembly may be attached to another substrate (e.g., a printed circuit board (PCB) or image sensor) with adhesive. The adhesive must be applied with precision and accuracy because uneven, unequal distribution of adhesive may cause tilt in the barrel/lens stack or tilt in the optical assembly, which can result in reduced image quality. In addition, if not controlled properly, adhesive may migrate to the active portion of the image sensor, which can result in the optical modules being unusable.